1. Field of the Invention
The present invention relates to a process and an apparatus for producing a metallic honeycomb body, in particular a honeycomb body for an exhaust system of an internal combustion engine. The invention also relates to a honeycomb body produced by the process or the apparatus. Such honeycomb bodies are used as carriers for catalytically active material and/or for adsorber material, as well as similar applications.
A distinction is drawn in particular between two typical forms of metallic honeycomb bodies. An early form, of which German Published, Non-Prosecuted Patent Application DE 29 02 779 A1, corresponding to U.S. Pat. No. 4,273,681, shows typical examples, is the helical form, in which, substantially, a smooth sheet-metal layer and a corrugated sheet-metal layer are placed on top of one another and wound helically. In another form, the honeycomb body is constructed from a multiplicity of alternately disposed smooth and corrugated or differently corrugated sheet-metal layers, with the sheet-metal layers initially forming one or more stacks, which are then intertwined. In the process, the ends of all of the sheet-metal layers come to lie on the outer side and can be joined to a housing or tubular casing, thereby forming numerous connections, which increase the durability of the honeycomb body. Typical examples of those forms are described in European Patent EP 0 245 737 B1, corresponding to U.S. Pat. Nos. 4,803,189; 4,832,998; 4,923,109; and 4,946,822 or International Publication No. WO 90/03220, corresponding to U.S. Pat. Nos. 5,105,539 and 5,135,794. Finally, there are also honeycomb bodies with a conical structure which, if appropriate, also have further additional structures for influencing flow. A honeycomb body of that type is described, for example, in International Publication No. WO 97/49905, corresponding to U.S. Pat. No. 6,190,784.
When producing catalyst carrier bodies, in particular for use in the treatment of exhaust gases from internal combustion engines, in particular from motor vehicles, it is necessary, due to the durability and load-bearing capacity which needs to be achieved, to join the various sheet-metal layers to one another and to the tubular casing as securely as possible. In the present text and in the text which follows below, the term sheet-metal layers is to be understood on one hand as meaning metallic sheet layers, but on the other hand also layers of a material through which a fluid at least partially flows. Materials of that nature through which a fluid at least partially flows are used to construct open particulate filters.
A brazing technique, in which the sheet-metal layers are preferably joined by a brazing process, is often used to join two sheet-metal layers. Various techniques, which preferably use brazing powder or brazing strips, but also brazing paste, are known for application of the brazing material. Processes for applying a bonding agent and brazing material to a metallic configuration which includes a honeycomb body are known, for example, from International Publication No. WO 89/11938, corresponding to U.S. Patent Application Publication Nos. U.S. 2001/0013390 A1 and U.S. 2002/0129890 A1, International Publication No. WO 94/06594, corresponding to U.S. Pat. No. 5,501,391, International Publication No. WO 93/25339, corresponding to U.S. Pat. No. 5,431,330, German Published, Non-Prosecuted Patent Application DE 29 24 592 A1, corresponding to U.S. Pat. Nos. 4,381,590 and 4,521,947, and German Published, Non-Prosecuted Patent Application DE 198 23 000 A1, corresponding to U.S. Pat. Nos. 6,425,517; 6,497,039; and 6,634,542.
Alternatively, it is known, for example, from European Patent EP 0 159 468 B1, corresponding to U.S. Pat. No. 4,602,001, to apply an additive, which substantially includes aluminum, in powder form using binder, adhesive or the like to join the sheet-metal layers to one another. The joint between the sheet-metal layers is produced by the formation of an alloy in the joining regions of the sheet-metal layers.
However, the step of applying a bonding agent and then applying the pulverulent additive or brazing material generally proves relatively complicated, in particular in terms of handling. Moreover, in particular brazed joints have drawbacks in terms of durability.